A border skirmish between high-powered Hamptons neighbors Terry Semel, the former Yahoo! chief, and investor Jonathan Sobel has exploded into a legal war waged on multiple fronts.

The property dispute has sparked four legal battles between the Amagansett neighbors, with Sobel most recently trying to scuttle Semel’s plan to build two homes on the $43 million, 8-acre spread he bought in 2005.

East Hampton zoning laws allow only one home per property.

“They’re saying Semel is an important guy who needs to have a guesthouse, but that’s not enough to ignore the law,” said Sobel attorney David Eagan.

Semel lawyer Bill Esseks told the zoning board last week that Sobel was just angry that Semel wouldn’t sell him a parcel between their spreads.

“My client has already put more than $5 million into this, and then they start this,” Esseks said.

The battle before the East Hampton Town Zoning Board of Appeals follows three other lawsuits.

Sobel wants title to three-quarters of an acre owned by Semel and is using a legal concept that lets property owners gain possession of land to which they’ve had exclusive access for 10 years.

He’s also suing Semel for clearing vegetation on the parcel, while Semel has sued Sobel over removal of a fence.

Oddly, Semel and Sobel have never actually met, their lawyers admitted.